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45250-AC9
Magnetic Resonance Imaging of Oil/Water Flow through Fractures

Matthew Becker, California State University (Long Beach)

Relative permeability of oil and water are not well understood in rock fractures.  The default approach has been to treat the fracture as a porous medium and use Buckley-Leverett models to predict fluid flow.  A rock fracture with a variable aperture may or may not be sufficiently analogous to interconnected pore network to justify this approach.  In this project, we measure pressure gradients across a rock fracture as aqueous and non-aqueous phase fluids are pushed through a core sample.  The fluid advance will be monitored simultaneously using magnetic resonance imaging.  Pressure responses will be interpreted using models of distributed capillarity in an essentially two-dimensional system. A comparison of theoretical and measured hydraulic gradient along with the phenomenological information provided by the time-lapsed imagery will allow a dynamic interpretation of relative permeability with fluid saturation.

In Year 1 we focused on the bench-top experimental set up in preparation for the MR imagery.  MR imaging time is expensive so it is important that pressures can be carefully measured before imaging begins.  After extensive testing of differential transducers, we determined that an inexpensive differential transducer (stated accuracy 22 Pa or 2.2 mm of water) should be sufficient for measuring capillary pressures in the flow experiments.  The transducer was tested using dodecane and FC-75, two non-soluble liquids with very different viscosity and densities.  Also in Year 1 we collected multiple samples of naturally fractured Potsdam sandstone cores from the Altona Flat Rock site near Plattsburgh, New York.  Using our handheld corer, however, proved difficult and we were able to collect cores of only 10 cm in length.  A sliding carriage was constructed by our machine shop to facilitate the extraction of longer rock cores (2.5 cm diameter by 15-20 cm in length).  This work was completed by a part-time non-thesis MA student, as we unable to recruit a full time thesis student.

In Year 2 a full time graduate student (Christopher Burke) was recruited for the project.  Bench top pressure measurements were made using phantoms constructed of Teflon tubing and variable aperture parallel plate ideal rock samples.  However, we had some problem in the MR lab where the length of tubing was sensitive to vibrations from the MR instrument.  The pressure transducers had to be moved closer to the sample, inside the MR coil. Further testing was required to assure that the magnetic field did not affect pressure measurements.  At this writing, we have collected MR images in real rock without pressure measurements, and MR imaging of Teflon phantoms with pressure measurements.

Year 3 will focus on MR imaging of real rock samples with pressure measurements.  After a sufficient dataset is collected, we will begin analysis of pressure and imagery by plotting measured differential pressure versus theoretical pressure predicted from capillary equations and measured in-situ rock aperture.

Expected Milestones:

• January, 2009               Complete MR imaging
• May 2009                    Complete theoretical analysis
• July 2009                     Draft publication sent to J. Geophysical Research.  

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